1. Field of the Invention
The present invention belongs to the field of relay protection automation in electrical power engineering, and in particular relates to an IEEE1588 negative testing method applicable to a slave clock device.
2. Background of the Invention
Since the smart substation requires a higher real-time performance, as well as the function of interactively collaborating with devices outside the substation, absolute time stamps are necessary. In a digital substation in which the process layer network adopts IEC61850 9-2, the IEEE1588 time synchronization is an applicable time synchronization. By using IEEE1588 timing, the dedicated timing network is omitted, the principle is simple, the implementation of the protocol takes up a small portion of the device resources, and the configuration is simple.
Currently, many electric power equipment manufacturers in our country have in succession launched research and production development regarding IEEE1588. The electric power companies have also carried out the interoperability test of IEEE1588 products. However, the conformity test of IEEE1588 protocol has just started in the industry of electric power. The key of the conformity test of IEEE1588 protocol is to optimize a conformity test case which has a comprehensive coverage, so as to efficiently find problems in realization of the IEEE1588 protocol.
The negative testing is opposite to the positive testing, and they are two important divisions in the test design. In simply words, the positive testing is to test whether the object under test have finished the job that it should have finished, while the negative testing to test whether the object under test have not performed the job that it should have not performed. In some documents the negative testing is called as a negative test, and the positive testing is called as a positive test. The positive testing case for IEEE1588 conformity test is easy to design, while the negative testing which simulates abnormalities is hard to design. This results in that there are relatively less negative testing in the IEEE1588 conformity test, the test has a narrow coverage, and it is impossible to efficiently guarantee the reliability of time synchronization for the slave clock device. Therefore, it is necessary to design an IEEE1588 negative testing case which has a comprehensive coverage to efficiently guarantee the reliability of time synchronization for the slave clock device.
In the negative testing project of the IEEE1588 protocol, testing the influence of abnormal messages on the slave clock under test is an important negative testing project. This kind of negative testing project aims to verify whether the message processing logic of the slave clock under test is correct, i.e., the slave clock under test should ignore (i.e., should not process) abnormal messages, so as to guarantee the reliability of the slave clock synchronous. The existing testing method is to firstly assemble an abnormal message in a frame (the abnormal message means a message which is not correct in format or content) and then send it to the slave clock device under test (DUT), and observe the response from the slave clock device. Nevertheless, this testing method finds difficulties in practice. Although the abnormal message is sent to the slave clock DUT, the response from the slave clock DUT is not obvious, and it is also very difficult to judge whether the slave clock DUT have ignored the abnormal message according to analysis of message interactive process. The reason lies in that both synchronous calculation process and delay calculation process in IEEE1588 protocol are periodical. Whether a frame of message is ignored does not have significant influence on the slave clock synchronization. Even the slave clock DUT is out of synchronization, there will be a process in which the deviation increases gradually. In view of the case that the existing testing method is difficult to test whether the message processing logic of the slave clock under test is correct, it is necessary to modify the existing testing method so as to be adapted to the actual test.